Matrix material for molding duplicate printing plates



United States Patent 3,377,950 MATRIX MATERIAL FOR MOLDING DUPLICATEPRINTING PLATES Vincent Squitieri, Billerica, and Dick J. Wollmar, SouthLincoln, Mass, assignors to W. R. Grace & Co., Cambridge, Mass., acorporation of Connecticut No Drawing. Continuation-impart ofapplication Ser. No. 330,659, Dec. 16, 1963. This application Apr. 6,1965, Ser. No. 446,119

2 Claims. (Cl. 101-4011) This is a continuation-in-part of copendingapplication Ser. No. 330,659, filed Dec. 16, 1963.

This invention relates to printing and more particularly to a matrix formolding plastic and rubber printing plates and a method of preparingsuch a matrix.

A matrix for the production of plastic and rubber printing platesgenerally comprises a base or support material impregnated with athermosetting resin and a layer of filled, heat-curing resin. Theaforementioned matrix must be capable of receiving and retaining anexact reproduction of the face of a printing form. The matrix, bearingan intaglio reproduction of the face of the printing form, can then beused to produce many identical printing plates.

In the past, matrices for the production of duplicate printing plateshave been prepared from a blank comprising fibrous board or basematerials which have been impregnated with a heat-curing phenolic resin,e.g., a phenol-formaldehyde resin. The face of the base materialgenerally comprises a layer of a filled, heat-curing resin which, whensubjected to the heat and pressure during the superposition of a typeform against said layer, would flow and compress sufficiently to receivean impression corresponding to the face of the printing form, and thenharden, maintaining the thus-formed impression.

The prior art matrices suffered from a number of drawbacks. For example,a release material, such as a silicone or graphite spray, had to beapplied to the surface of the matrix prior to the formation of theduplicate plate in order to provide ready, uniform release of theduplicate plate. In the formation of the intaglio reproduction on thesurface of the matrix, a certain degree of nonuniformi-ty was introducedinto the surface of the heat-cured resin. Such nonuniformity may bemanifested in extreme thinness of the layer, pin-holes, or breaks in thesurface, particularly where sharp edges and indentations were formed insaid surface and where the surface layer had been extended beyond itsplastic flow limit. The rubber or plastic material of the duplicateprinting plate would readily penetrate such openings in the surface andadhere or bond to the phenolic-fiber base material. When the matrix andprinting plate were separated, a portion of the duplicate plate materialwould adhere to the matrix, thereby forming an imperfection in theduplicate plate which would become readily apparent and objectionableand in some cases unusable when the duplicate plate was made inprinting. The above-described adherence of the duplicate plate materialto the matrix is generally referred to as picking. The prior artmatrices were subject to warp and one dimensional shrink. The price perunit area of the matrices was also relatively high due to the highdensity of the matrix. The thickness was approximately 0.090 to 0.200inch, and the compression was about 30 to 40 percent at 500 p.s.i.

A molded matrix has now been found which is not subject to the failingsof the prior art materials and which also possesses a number ofunexpected advantages. The laminated blank of the present inventioncomprises a compressible fibrous base material which has been im-3,377,950 Patented Apr. 16, 1968 pregnated with a thermosetting materialand a surface coating or layer on one face of said base comprising ablend of at least two polymers; at least one polymer being thermoplasticand at least one being a heat cross-linkable acrylate polymercomposition. The heat to accomplish the cross-linking is supplied to theblanks from the heated type face when the molded blank is formed.

Acrylate compositions which cross-link upon the action of heat are wellknown to the art. Such cross-linking polymers generally compriseinterpolymers of acrylates such as methyl or ethyl acrylate with atleast two comonomers containing pendant reactive groups. As examples ofsuch pendant reactive groups, mention may be made of carboxylic acidgroups, hydroxyl groups, and methylolamide groups which react with otherpendant groups such as epoxide or glycidyl groups. As an example of anacrylate polymer capable of internally cross-linking, mention may bemade of a glycidyl acrylate/methyl methacrylate/aorylic acid copolymer.In addition to the above-described internal cross-linking mechanism,acrylate polymers may also be cured or cross-linked by the addition ofan external cross-linking material to the polymer composition, e.g., theaddition of formaldehyde to an acrylamide/acrylate copolymer. In theabove-described cross-linking compositions, the application of heatinitiates the reaction between the pendant reactive groups. Examples ofother suitable cross-linking acrylates may be found in U.S. Patent Nos.2,580,901; 2,857,354; 2,870,116; 2,870,117; and 2,931,742, and otherpatents.

Preferred thermoplastic polymers are polyethylene and polyurethanes.

The surface :layer of the blank is, therefore, one which, during theimpression by the type form, will be crosslinked by heat into acontinuous film bearing a reproduction of the type form.

The thermoplastic materials, which alone would be too weak, impartflexibility to the layer while the heat crosslinkable polyacrylateimparts strength to the layer.

The combination of the thermosetting impregnant in the base and thenovel surface coating of the present invention which is compatible withthe impregnant permits the formation of an accurate, stable impressionin the matrix with a minimization of the picking problem. Thethermoplastic properties of the films permit the films to readily flowand, at the same time, maintain continuity while the impression is beingmade, thereby eliminating the formation of stresses and the possibilityof rupture of the film layer which could lead to picking, while thecross-linking affords stabilizational strength to the structure. Suchsurface layers also lack porosity. The film materials of the presentinvention are heat stable to temperatures well in excess of temperaturesnormally utilized in molding duplicate plates. Therefore, thepossibility of exceeding the plastic flow limit of the surface layer isremote in the present invention. The compatability of the impregnant andthe surface layer provides for good adhesion and mechanical interlockingand prevents displacement or separation of the film layer on the basematerial thereby retaining accuracy in the reproduction even throughoutthe preparation of many duplicate plates. By using less dense materials,the instant matrices can be formed with only 0.080 of an inch thick,While at the same time providing approximately 50 to 60 percentcompression as compared with about 30 to 40 percent for prior artmaterials. The shrink of the matrices of the present invention is notappreciable; therefore, distortion of the duplicate plates formed fromthe matrices is minimized. The resin in the base material can be curedin approximately half the time required for the prior art materials dueto the use of the thinner board.

One of the most important advantages of the present invention is theself-contained release characteristics of the film layers of the presentinvention which makes unnecessary the use of a release compound and theattendant problems of applying a uniform and complete layer of saidrelease compound to the matrix surface.

The preferred thermosetting resin for use in impregnating the fibrousbase material is a blend of low residual phenol-formaldehyde resin andbutadiene/acrylonitrile latex suspended in water. The most desirablebalance of strength and flexibility has been found in the phenolic tobutadiene/acrylonitrile ratio of 9 to l. The solids (resin) to fiberratio in the base material preferably range from 0.45 to 0.60. Otherthermosetting resins known to the art, such as phenolic resins, may beused as the impregnant in the base material.

In a preferred embodiment both of the components of the polymeric systemare cross-linked in order to provide an interlinking system. This may beaccomplished by the addition of a cross-linking agent such as hydrazinefor polyethylene. The cross-linking of polyethylene with hydrazine andother materials is described in US. Patent No. 3,171,830. Othercross-linking agents for polyethylene known to the art are alsoemployed.

The matrix base material comprises a resinized paperboard consisting ofa heat-curing phenolic resin and fibrous material having a solids-fiberratio preferably ranging from 0.45 to 0.60. The fibrous material ispreferably a combination of wood flour and cellulosic fibers. The basematerial may be formed by a process which involves the suspension offinely-divided particles of the resin in the beater of a paper machinewith a substantial portion of paper pulp. This combination is thenthoroughly mixed and suspended in water and the mixture is fed to apaperboard-making machine which forms the material as a sheet ofcomparatively low density. The sheet is then dried until the residualmoisture or volatile matter is not more than about 4 percent. Suchresinized paperboard is known to the art as Premix Board and RogersBoard.

The base material may also be formed from a stack of impregnated softpaper or pulp. This can be accomplished by conveying uniform sheets ofpressed sulfite pulp through a bath of the phenolic resin-in-watersolution. When such a water solution has a solids content of about 20 to30 percent, the viscosity is low and penetration of the pulp issufiiciently complete. The impregnated web of sulfite pulp is drawnbetween squeeze rolls and is then conveyed through a drying oven toevaporate the water and to give the phenolic resin a suitable precure.

The base material may also be formed by conveying a wet sheet of paperpulp through a water bath containing the phenolic resin. Afterpenetration of the fibers of the pulp with the phenolic solutions, thesheet is pressed between squeeze rolls and then passed into an oven inorder to reduce the moisture content to the desired level.

The novel surface layer of the present invention may be applied to thebase material from a dispersion or solution and which is then dried toprovide the film layer. Coating methods known to the art may be used inapplying the dispersion, e.g., air knife coating, floating knifecoating, and curtain coating. Prior to coating the base with thepolymeric dispersions, it is preferable to precoat the base with acommon clay or pigment binder to provide optimum coating and adhesion.

The polyethylene is preferably applied from an emulsion ranging from 20to 50 percent solids, and has a particle size less than 0.05 micron anda viscosity ranging from 10 to 200 cps, at 25 C.

The polyurethanes are elastomeric materials which are prepared by thereaction of polyisocyanates and polyhydroxy compounds to form longchains which are then chain extended and cross-linked. The polyurethanesgenerally have a specific gravity ranging from 1.20 to 1.26.

The polyurethanes are also preferably employed as emulsions.

The blend of polymers is prepared by physically mixing the solutions ordispersions of the polymers.

Preferably, the thermoplastic polymer and heat crosslinkablepolyacrylate are present in a 1 to 1 solids ratio; however, it should beunderstood that satisfactory surface layers can be prepared within therange of 5 to 1 and 1 to 5 solids ratio. The polymers are preferablycoated so as to provide a 10 to 25 lbs. coating of solids per ream(3,000 sq. ft).

The following nonlimiting examples illustrate the novel polymericcompositions suitable for preparing the novel surface layers of thepresent invention. The percentages are understood to be on a weightbasis.

Total solids, 40%.

Polyacrylate (AC-201, trade name for Rohm and Haas Co., Philadelphia,Pa., aqueous cross-linking polyacrylate emulsion) 50 'Density, 1.1.Total solids, 46%.

The above compositions were used to prepare blanks by coating abaseboard composed of 67% cotton linters and 33% phenol-formaldehyderesin with a 2-mil layer (dry) of the composition. Satisfactory resultswere achieved when the blanks were used to form a molded matrix for theproduction of duplicate printing plates.

It may be desirable, but it is not necessary, to add other materialssuch as emulsifiers or wetting agents to the coating composition inorder to provide greater ease in coating the fibrous base material.

The surface layers of the present invention are 1 to 3 mils inthickness. Preferably 1 and 2 mil layers are employed. Two or morecoatings may be necessary in order to provide the desired thickness.Layers in excess of 3 mils are undesirable due to excessive cost andinability to retain fine line screen reproductions with shallow relief.

In forming a matrix from a blank of the present invention, a metal typeform is preheated to approximately 300 to 350 F., preferably 300 F., andplaced in contact with the surface of the blank. A hydraulic press withplatens heated to 300 to 350 F. holds the blank and type form forcedtogether for a time sufiicient to cure the thermosetting resin in thebase material, generally around 5 minutes. The matrix bearing an exactintaglio reproduction of the face of the type form is then removed andis ready to be used informing duplicate printing plates.

We claim:

1. A laminated blank for molding to form a matrix for the production ofduplicate printing plates comprising a fibrous base material impregnatedwith a thermosetting resin and having on one face of said face materiala polymeric layer comprising a blend of at least two polymers, at leastone polymer being a cross-linkable polyethylene polymer and at least onepolymer being a heat cross- 6 linkable acrylate polymer and said blendincluding a cross- References Cited linking agent for said polyethylene.UNITED STATES PATENTS 2. A laminated matrix for the production ofduplicate printing plates comprising a fibrous base impregnated with 099 5/ 195 filiggms 1014014 XR a thermosettin resin and a surface coatingon one side of 5 2580'901 1/1952 Enckison et 260-7754 2,703,051 3/ 1955Richardson I 101401.1

said base comprising a blend of at least two polymers, at

least one polymer being a cross-linked polyethylene poly- DAVID KLEIN,Primary Examiner. mer and at least one polymer being a cross-linkedacrylate polymer; said matrix bearing an intaglio reproduction of ROBERTPULFREY Exwmmer' the face of a printing form. 10 J. A. BELL, AssistantExaminer.

2. A LAMINATED MATRIX FOR THE PRODUCTION OF DUPLICATE PRINTING PLATESCOMPRISING A FIBROUS BASE IMPREGNATED WITH A THERMOSETTING RESIN AND ASURFACE COATING ON ONE SIDE OF SAID BASE COMPRISING A BLEND OF AT LEASTTWO POLYMERS, AT LEAST ONE POLYMER BEING A CROSS-LIKED POLYETHYLENEPOLYMER AND AT LEAST ONE POLYMER BEING A CROSS-LINKED ACRYLATE POLYMER;SAID MATRIX BEARING AN INTAGLIO REPRODUCTION OF THE FACE OF A PRINTINGFORM.